1. Field of the Invention
This invention relates to methods for sterilizing packaged goods and in particular towards relatively low temperature sterilization methods for packaged goods.
2. The Related Art
Sterilization of packaged goods is necessary to destroy harmful bacteria or other organisms living inside of the package. There are numerous methods used to sterilize packages and/or the contents of a package, including steam sterilization, gas sterilization, and irradiation. Other techniques include exposing the packaged goods to heat in the presence of water, and exposing the packaged goods to heat in the presence of an anti-bacterial agent within the container.
Steam sterilization is typically carried out in an autoclave, a tower autoclave, or a rotomat and employs saturated steam under pressure. The autoclave is commonly operated at a temperature of about 120.degree. C. Due to this relatively high temperature, many types of articles cannot be treated in such a manner. For other articles, the desired packaging cannot survive such conditions. As a result, such articles may be steam sterilized and then packaged.
Gas sterilization is commonly carried out using gases such as ethylene oxide or propylene oxide. A variety of gas sterilization processes have been carried out, for example, using the steps of pre-humidification, heating and evacuation of a chamber, and exposure to a high concentrations of gas for a period of up to 20 hours. Gas sterilization may lead to the formation of undesirable components such as glycol in the presence of water.
Irradiation has also proven effective in sterilizing packaged goods, including the use of gamma radiation at levels of about 0.05 to 2.0 megarads (mR). However, a drawback to the irradiation method is the high cost of the procedure. Such high cost is dictated by factors including the equipment used and the numerous regulations which must be followed to insure safety. Due to the costs involved, there are relatively few irradiation facilities for performing sterilization, and therefore the time necessary to ship goods, have them irradiated, then shipped back to a manufacturer can be extensive.
U.S. Pat. No. 3,618,283 to Moore et al. discloses a method for sterile packaging of articles such as catheters, hypodermic needles, sutures, etc., in a flexible container. The method requires the presence of a liquid anti-bacterial agent which contacts the exposed surfaces of the container and the contents of the container. The container must be flexible so that it can be kneaded, rolled, or otherwise worked in order to completely contact all interior surfaces of the container and all exposed surfaces of the articles with the anti-bacterial solution. After all surfaces have been contacted, the container is heated. The anti-bacterial agents which may be used include a soap solution with 1 to 2% hexachlorophene, a solution of an iodophor, a 3% solution of parachloromethahexanol, a 1 to 5% solution of Merthiolate, and an aqueous 3% solution of Zephiran.
U.S. Pat. No. 3,754,368 to Moore et al. discloses a method of sterile packaging including sealing a product comprising a liquid, which is at least predominantly water, in a container capable of withstanding a temperature of 212.degree. F. at atmospheric pressure. Next the container and its contents are heated for at least 24 hours and up to 200 or more hours, at a temperature above 170.degree. F. and below 212.degree. F. and below the boiling temperature of the liquid.
Depending on the goods to be sterilized, and the packaging desired to be used, the temperature at which sterilization is carried out can be a critical feature of the sterilization process. For example, certain cosmetics are made from emulsions or solutions which will separate at temperatures such as those noted above. Other items will melt or be otherwise chemically altered at such temperatures. For example, certain packaging such as shrink-wrap or other polymer packaging often have a relatively low melting point.
It would be desirable to have a relatively low temperature method for sterilization of a wide range of articles and packages, without the need for exposure to anti-bacterial agents. It would also be desirable for the sterilization method to be inexpensive, and safe from dangers such as those which could occur during the radiation process. Embodiments of the present invention are directed towards these and other objectives.